1. Field of the Invention
The present invention relates to a method for manufacturing a substrate including a semiconductor layer that is used for manufacture of a semiconductor device.
Note that a semiconductor device in the present specification generally indicates a device capable of functioning by utilizing semiconductor characteristics, and electro-optic devices, semiconductor circuits, and electronic devices are all semiconductor devices.
2. Description of the Related Art
Integrated circuits using an SOI (Silicon on Insulator) substrate where a thin single crystalline semiconductor layer is formed on an insulating surface, instead of a bulk-like silicon wafer, have been developed. Since parasitic capacitance between a drain of a transistor and a substrate is reduced by using the SOI substrate, the SOI substrate has been attracted attention as one improving performance of semiconductor integrated circuits.
A Smart Cut method is known as one of methods for manufacturing an SOI substrate. An outline method for manufacturing an SOI substrate by a Smart Cut method is described below. Hydrogen ions are implanted into a silicon wafer to form a microbubble layer at a predetermined depth from the surface. The silicon wafer into which the hydrogen ions are implanted is bonded to another silicon wafer with a silicon oxide film interposed therebetween. After that, by performing heat treatment, the microbubble layer is to be a cleavage plane, and the wafer into which the hydrogen ions are implanted is separated in a thin film state. A Smart Cut method may be referred to as a hydrogen ion implantation separation method.
An SOI substrate where a silicon layer separated from a silicon wafer is bonded to a glass substrate is known (see Reference 1: Japanese Published Patent Application No. H11-097379 and Reference 2: Japanese Published Patent Application No. 2005-252244). In Reference 1, a semiconductor substrate after the separation step is reused. After the silicon layer is separated from a single-crystal silicon substrate, the silicon layer bonded to a base substrate is planarized by mechanical polishing.
In Reference 2, after the separation step, a Si thin film bonded to a glass substrate is irradiated with laser light to be recrystallized, so that crystalline quality of the Si thin film is improved.